The Purification and Properties of a Ribonuclease from Salmonella typhimurium Extract

Abstract

A ribonuclease has been purified about 140-fold from extracts of Salmonella typhimurium through ammonium sulfate fractionation, gel filtration, and DEAE-cellulose chromatography. The optimum pH for the hydrolytic breakdown of RNA is 7. The enzyme hydrolyzes polyadenylic acid (poly A), polycytidylic acid (poly C), and polyuridylic acid (poly U) at much faster rates than transfer RNA. Polyinosinic acid (poly I) was not hydrolyzed at all. Higher concentrations of poly A and poly U (above 200 µg per ml) were inhibitory. A mixture of poly A and poly U in the proportion 1:2, which is known to produce maximum secondary interaction, is also inhibitory. These results indicate that the secondary structures of nucleic acids interfere with the action of the nuclease. The first product of hydrolysis is a 2′,3′-cyclic nucleotide which is poorly hydrolyzed to the 3′-nucleotide. The enzyme behaves as an endonuclease. The properties of the S. typhimurium nuclease have been compared with those of RNase I of Escherichia coli. Although there are some differences, the S. typhimurium nuclease is like RNase I in its mode of action.